Overview for swales Revision as of 15:46, 5 March 2013 by PLeegar (talk | contribs) (Created page with " ==Suitability== ===General=== <p>Filtering practices include media filters (surface, underground, perimeter), vegetative filters (filter strips,...")
Contents
Suitability
General
Filtering practices include media filters (surface, underground, perimeter), vegetative filters (filter strips, grass channels), and combination media/vegetative filters (dry swales). Media and media/vegetative filters operate similarly and provide comparable water quality capabilities as bioretention. Vegetative filters are generally more suitable as pre-treatment practices, but in some situations can be used on a stand alone basis.
Filtering practices have widespread applicability and are suitable for all land uses, as long as the contributing drainage areas are limited (e.g., typically less than 5 acres). Media filters are not as aesthetically appealing as bioretention, which makes them more appropriate for commercial or light industrial land uses or in locations that will not receive significant public exposure. Media filters are particularly well suited for sites with high percentages of impervious cover (e.g., greater than 50%). Media filters can be designed with an underdrain, which makes them a good option for treating potential stormwater hotspots (PSHs). They can also be installed underground to prevent the consumption of valuable land space (often an important retrofit or redevelopment consideration). Vegetative filters can be incorporated into landscaped areas, providing dual functionality.
Suitability
General
Filtering practices include media filters (surface, underground, perimeter), vegetative filters (filter strips, grass channels), and combination media/vegetative filters (dry swales). Media and media/vegetative filters operate similarly and provide comparable water quality capabilities as bioretention. vegetative filters are generally more suitable as pre-treatment practices, but in some situations can be used on a stand alone basis.
Filtering practices have widespread applicability and are suitable for all land uses, as long as the contributing drainage areas are limited (e.g., typically less than 5 acres). Media filters are not as aesthetically appealing as bioretention, which makes them more appropriate for commercial or light industrial land uses or in locations that will not receive significant public exposure. Media filters are particularly well suited for sites with high percentages of impervious cover (e.g., greater than 50%). Media filters can be designed with an under-drain, which makes them a good option for treating potential stormwater hotspots (PSHs). They can also be installed underground to prevent the consumption of valuable land space (often an important retrofit or redevelopment consideration). Vegetative filters can be incorporated into landscaped areas, providing dual functionality.
Function Within Stormwater Treatment Train
Media filtration systems are designed primarily as off-line systems for stormwater quality and typically are used in conjunction with another structural control. Vegetative filters, designed as grass channels or swales, may be the main form of conveyance between or out of BMPs, as well as providing treatment for stormwater runoff.
MPCA Permit Applicability
One of the goals of this Manual is to facilitate understanding of and compliance with the MPCA Construction General Permit (CGP), which includes design and performance standards for permanent stormwater management systems. These standards must be applied in all projects in which at least one acre of new impervious area is being created, and the permit stipulates certain standards for various categories of stormwater management practices.
For regulatory purposes, filtration practices fall under the “Infiltration / Filtration” category described in Part III.C.2 of the permit. If used in combination with other practices, credit for combined stormwater treatment can be given as described in Part III.C.4. Due to the statewide prevalence of the MPCA permit, design guidance in this section is presented with the assumption that the permit does apply. Also, although it is expected that in many cases the filtration practice will be used in combination with other practices, standards are described for the case in which it is a stand alone practice.
The following terms are thus used in the text to distinguish various levels of filtration practice design guidance:
REQUIRED:Indicates design standards stipulated by the MPCA Permit (or other consistently applicable regulations).
HIGHLY RECOMMENDED: Indicates design guidance that is extremely beneficial or necessary for proper functioning of the filtration practice, but not specifically required by the MPCA permit.
RECOMMENDED:' Indicates design guidance that is helpful for filtration practice performance but not critical to the design.
Of course, there are situations, particularly retrofit projects, in which an infiltration facility is constructed without being subject to the conditions of the MPCA permit. While compliance with the permit is not required in these cases, the standards it establishes can provide valuable design guidance to the user. It is also important to note that additional and potentially more stringent design requirements may apply for a particular infiltration facility, depending on where it is situated both jurisdictionally and within the surrounding landscape.